1. Technical Field
The present invention relates to a method and apparatus for changing the direction of motion of a pallet moving on wheels at the end of a travelator or equivalent.
2. Related Art
Like escalators, travelators are conveying devices primarily designed to move people and their goods. They differ from escalators, e.g., in that they are often operated in a substantially horizontal orientation or in an orientation somewhat inclined, e.g., typically by about 1-15° relative to their direction of motion. Successive steps or pallets typically form a substantially even and rectilinear conveyor track instead of stair-like steps as in escalators. Instead of successive steps, the travelator may also have a continues belt, in which case the travelator resembles a belt conveyor. Travelators are also referred to as moving sidewalks and autowalks. Travelators differ from bulk and freight conveyors essentially in that travelators are designed by considering special requirements related to transportation of people, such as convenience of use and safety.
In prior art travelators, the structure is embedded in the ground or in the floor of a building. In such solutions, pits about one meter deep and several meters long are provided at either end of the travelator to accommodate the machinery of the travelator structure and the pallet turn-around mechanism. The sinking depth required in the middle part of the travelator is about half a meter. A drawback with this type of travelator construction is that they require heavy and fixed structures in the floor of the space around them, which is why they have to be taken into account at the time when the building is being designed. A further drawback is that moving such fixed structures from one place to another as required when the traffic needs change is completely impossible.
In prior art solutions, the pallet track typically comprises pallets having a length of about 15 to 40 cm, corresponding to escalator steps. The pallets are connected together as a chain, normally using a chain or, e.g., a cogged belt, and the whole belt is driven around by means of a machine and a chain wheel, so that the upper pallets in the chain, being supported by rollers, move on a special track.
At the end of the pallet track, the pallets are turned upside down around a wheel of a large diameter and return back to the beginning of the track below the track. At the beginning end the returning pallets are again turned around to their normal transport position and continue moving on the track towards the terminal end of the track.
One of the problems with such a prior art solution is that the pallets are turned around at the ends of the track, requiring the space where the pallets are turned to have a depth at least equal to the length of the pallet. In practice, however, the depth is about 1.5 to 2 times the length of the pallet because, otherwise, the operation will not be smooth enough.
Patent document No. GB2299316 depicts in FIG. 1/3 a structure of the above-mentioned type as an example of the prior art. In addition, this patent document discloses a travelator construction wherein the pallets are guided at their turning points by fixed tracks keeping them continuously in a horizontal orientation. Thus, the pallet is not turned upside down at the turning point. The pallets are actually guided along a curved track by wheels placed in the forward part of the pallet as seen in the direction of motion while the wheels in the rear part remain substantially free. However, the solution according to this patent document involves the problem that there are so-called dead centers at the end points of the track where the position of the pallet is not completely precisely defined. For this reason, the pallet may get jammed at the dead center, in which case the whole apparatus will stop due to the operating disturbance and may even be damaged. The risk of pallets getting jammed is increased by the running clearances, non-ideal track design and wear of the mechanism.